The number of HIV (human immunodeficiency virus)-positive individuals has risen over recent years mainly because combination antiretroviral therapy (cART) is helping these patients live longer. However, the prevalence of HIV-Associated Neurocognitive Disorders (HAND) has also risen since cART drugs in general do not effectively cross the blood-brain-barrier. To address this issue, we propose to evaluate a new type of treatment targeted for HAND. In patients with HAND and in animal models of the disease process, we and others have accumulated evidence that neurons are damaged. Additionally, emerging evidence from our laboratory and others suggests that adult neuroprogenitor cells (aNPCs) are also decreased in the brains of patients with NeuroAIDs. Active neurogenesis normally occurs throughout life in the dentate gyrus in the hippocampus. Newly generated neurons are incorporated into the neural network, contributing to certain types of learning and memory. Intriguingly, hippocampal neurogenesis is significantly altered in several neurodegenerative diseases in addition to HAND. Recently, we reported that the HIV-envelope glycoprotein gp120, which is associated with HAND pathogenesis, inhibits proliferation of adult neural progenitor cells in vitro and in vivo in the dentate gyrus of the hippocampus in a NeuroAIDS rodent model, the HIV/gp120- transgenic mouse. As potential treatment, we and our collaborators have synthesized new peptide inhibitors of chemokine receptors (CXCR4 and CCR5, which are co-receptors for HIV/gp120), and found that these novel synthetically and modularly modified (SMM)-chemokines block the inhibitory effect of gp120 on neural progenitor proliferation in vitro. Here, we propose to investigate the effectiveness of SMM-chemokines in vivo, beginning with new, very selective and non-toxic CXCR4 antagonists. In particular, we propose to investigate whether transnasal (also called intranasal) application of SMM-chemokines can prevent the decrease in proliferation of adult neural progenitors in mouse models of NeuroAIDS. Notably, we have recently shown that transnasally administered-peptides are preferentially delivered to the brain, and other peptides have been approved in humans by the FDA for brain delivery in this fashion. We list the following Specific Aim: (1) To investigate whether transnasal application of SMM-chemokine analogs protects adult neurons and restores the proliferation of adult hippocampal progenitors in HIV/gp120-transgenic mice. Note that in future work, we plan to test for 'generalization' of the effect of the SMM-chemokine analogs by investigating whether transnasal application of SMM-chemokine analogs also protects neurons and restores the proliferation of adult hippocampal progenitors in a second NeuroAIDS model, consisting of NOD/scid-IL- 2Rgcnull mice that are reconstituted with human hematopoietic CD34+ stem cells and then infected with HIV-1. This model, as developed by our collaborator Dr. Howard Gendelman and colleagues, while more difficult to utilize, closely mimics human HAND progression and cognitive dysfunction.